Surface inspection apparatus and method thereof

ABSTRACT

A defect inspection apparatus including: a first illumination optical system which is configured to illuminate the inspection area on a sample surface from a normal line direction or a direction near thereof with respect to said sample surface; a second illumination optical system which is configured to illuminate said inspection area from a slant direction with respect to said sample surface; a detection optical system having a plurality of first detectors which are located, in front of, on the sides of, and behind said inspection area, respectively, with respect to the illumination direction of said second illumination optical system, and where the regular reflected light component, from said sample surface, by illumination light of said second illumination optical system, is not converged; and a signal processing system which is configured to inspect a defect, upon basis of signals obtained from said plurality of first detectors.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 13/114,160, filedMay 24, 2011 which is a continuation of U.S. application Ser. No.12/196,647, filed Aug. 22, 2008 (now U.S. Pat. No. 7,952,085), which isa continuation of U.S. application Ser. No. 11/657,455, filed Jan. 25,2007 (now U.S. Pat. No. 7,417,244), which is a continuation of U.S.application Ser. No. 11/104,621, filed Apr. 13, 2005 (now U.S. Pat. No.7,242,016), which is a continuation of U.S. application Ser. No.09/791,742, filed Feb. 26, 2001 (now U.S. Pat. No. 6,894,302). Thisapplication relates to and claims priority from Japanese PatentApplication No. 00-068593, filed on Mar. 8, 2000. The entirety of thecontents and subject matter of all of the above is incorporated hereinby reference.

BACKGROUND OF THE INVENTION

The present invention relates to a surface inspection apparatus and amethod thereof for discriminatingly inspecting defects such as scratchesand foreign objects that arise in the flattening process in whichpolishing or grinding working technique is applied in semiconductormanufacturing processes or magnetic head manufacturing processes.

As for the prior art for discriminatingly inspecting a foreign objectthat adheres on a semiconductor wafer on which a circuit pattern hasbeen formed from the circuit pattern, Japanese Unexamined PatentPublication No. H3-102248 (prior art 1) and Japanese Unexamined PatentPublication No. H3-102249 (prior art 2) have been known. In detail, amethod is described in the prior art 1 and the prior art 2 in which aforeign object on a semiconductor substrate is detected by means of afirst photoelectric conversion element with emphasis by use of a slantillumination, and an edge of a circuit pattern that is the background onthe semiconductor is detected by means of a second photoelectricconversion element with emphasis by use of an epi-illumination, theforeign detection signal obtained from the above-mentioned firstphotoelectric conversion element is divided by the detection signalobtained from the second photoelectric element to thereby emphasize theforeign object detection signal, and thus the foreign object isdetected.

As for the prior art for discriminatingly inspecting adherent foreignobjects on the silicon wafer surface from the crystalline defect on thesurface, Japanese Unexamined Patent Publication No. H9-304289 (prior art3) has been known. In detail, a discriminating inspection method isdescribed in the prior art 3, in which an inspection apparatus isprovided with a low angle light receiving system that makes an elevationangle of equal to or smaller than 30 degrees with respect to the surfaceof the silicon wafer and a high angle light receiving system that makesan elevation angle of larger than that of the low angle light receivingsystem, the scattered light obtained by irradiating a laser light ontothe surface of the silicon wafer approximately perpendicularly isreceived by the low angle light receiving system and the high anglelight receiving system, wherein the light received only by the highangle light receiving system is attributed to the crystalline defect,and the light that is received by both the low angle light receivingsystem and the high angle light receiving system is attributed to theadherent foreign object.

As for the prior art for discriminatingly inspecting the foreign objector flaw on the surface of a semiconductor wafer from a small dot dimplethat is too small to cause the problem in forming of a circuit patternwithout mis-discrimination, Japanese Unexamined Patent Publication No.H11-142127 has been known (prior art 4). In detail, an inspection methodis described in the prior art 4, in which a low incident angle light anda high incident angle light having wavelengths that are different eachother are irradiated in focus on the same point on the surface of asemiconductor wafer with a low incident angle and a high incident anglerespectively, the scattered light of two wavelengths from the focusedpoint is received separately and photoelectrically converted, and thusthe foreign object and the flaw is discriminated from the dot dimple onthe surface of the semiconductor wafer, wherein the intensity differencebetween signals is utilized, that is, the principle that the intensityof the light irradiated with a low incident angle and scattered from thedot dimple is weak is utilized.

Aside from the above, CMP (Chemical Mechanical Polishing) has been knownas a typical (flattening) work technique applied on a work target (forexample, insulating film) in the semiconductor manufacturing process ormagnetic head manufacturing process. CMP is a (flattening) technique inwhich free abrasive grains consisting of a material such as silica isspread on a polishing pad and the surface of the work target ispolished. Another grinding work technique has been known, in which awork target is polished with use of a pad on which grinding grainsconsisting of a material such as diamond are embedded fixedly. In suchpolishing or grinding process, scratches having various configuration,that are polishing flaw or grinding flaw, can be formed on the surfaceof a work target (for example, an insulating film on a semiconductorsubstrate (wafer)). If scratches having various configuration are formedon the surface of a work target in the semiconductor manufacturingprocess or the magnetic head manufacturing process as describedhereinabove, a scratch causes insufficient etching in wiring forming andcauses the defect such as short-circuit. To eliminate such defect, it isnecessary that the polished wafer surface or ground surface is observedafter polishing or grinding to monitor the occurrence of scratcheshaving various configuration, and polishing condition or grindingcondition must be reviewed correspondingly to the configuration ofscratches if the scratch occurs frequently. Furthermore, the foreignobject also causes the defect such as defective insulation andshort-circuit of wiring to be formed thereon.

If the foreign object occurs frequently, a countermeasure such ascleaning of an equipment is required, and at that time thecountermeasure is different from that for scratching. In other words, itis required to monitor discriminatingly between the foreign object andscratch having various configuration, and to apply a countermeasurerelevant to the foreign object or scratch in polishing process orgrinding process applied on a work target (for example, an insulatingfilm on a semiconductor substrate).

However, any of the prior arts 1 to 4 does not involve inspection fordiscriminating between the scratch having various configuration andadherent foreign object on the surface of a work target in polishingprocess or grinding process applied on the work target (for example, aninsulating film on a semiconductor substrate).

Generally, because the width W of the scratch having variousconfiguration ranges as small as from 0.2 μm to 0.4 μm, and the depth Dranges as very shallow as from several nm to the deepest 100 nm, aworker visually discriminates between the scratch having variousconfiguration and the foreign object by use of an electron microscopeconventionally, but such visual observation requires much time. As theresult, the countermeasure for scratch or foreign object is deviseddelayingly, and many wafers are polished under bad condition to resultin much loss of profit.

SUMMARY OF THE INVENTION

The invention provides a surface inspection apparatus and a method forinspecting the surface of a sample that are capable of inspectingdiscriminatingly between the scratch of various configuration and theadhered foreign object that occur on the surface of a work target whenthe work target (for example, an insulating film on a semiconductorsubstrate) is subjected to polishing process such as CMP or grindingprocess in semiconductor manufacturing process or magnetic headmanufacturing process.

Furthermore, the present invention provides a semiconductor substratemanufacturing process in which the defect is inspected discriminatinglybetween the scratch of various configuration and the adhered foreignobject that occur on the surface of a work target when the work target(for example, an insulating film on a semiconductor substrate) issubjected to polishing process such as CMP or grinding process insemiconductor manufacturing process or magnetic head manufacturingprocess with the total inspection or sufficiently frequent samplinginspection, and as the result the semiconductor substrate having nodefect is efficiently manufactured with high reliability.

Furthermore, the present invention provides a surface inspectionapparatus and a surface inspection method for inspecting the defectlocated near the wafer edge of the work target.

In detail, in the present invention, the surface inspection apparatus isprovided with a stage on which an inspection target is placed, anillumination optical system having an epi-illumination system forepi-illuminating the inspection target placed on the stage and a slantillumination system for slant-illuminating the surface of the inspectiontarget placed on the stage, a detection optical system having a firstconverging optical system for converging the first scattered light thatcomes in the direction of the first desired angle with respect to thesurface of the inspection target out of the first reflected lightemitted from the inspection target epi-illuminated by means of theepi-illumination system of the illumination optical system and thesecond scattered light that comes in the direction of the first desiredangle out of the second reflected light emitted from the inspectiontarget slant-illuminated by means of the slant illumination system ofthe illumination optical system and having a first photoelectricconversion means for receiving the first and second scattered lightsconverged by means of the first converging optical system to therebyconvert the received lights to the first and second luminance signals, acomparison discrimination unit for discriminating the defect on theinspection target based on the relation between the first luminancesignal and the second luminance signal that have been converted by meansof the photoelectric conversion means of the detection optical system,and an output unit for supplying the result obtained by means of thecomparison discrimination unit.

Furthermore, in the present invention, the surface inspection apparatusis provided with a stage that is movable in at least two-dimensionaldirection on which an inspection target is placed, an illuminationoptical system having an epi-illumination system used forepi-illuminating the inspection target placed on the stage and having aslant illumination optical system used for slant-illuminating thesurface of the inspection target, a reflected light detection systemhaving a first reflected light detection unit for detecting thereflected light reflected from the inspection target that isepi-illuminated by means of the epi-illumination system of theillumination optical system and having a second reflected lightdetection unit for detecting the reflected light reflected from theinspection target that is slant-illuminated by means of the slantillumination system of the illumination optical system, a defectdetection system for detecting the defect on the inspection target byuse of the output signals of the first reflected light detection unitand the second reflected light detection unit of the reflected lightdetection system, a defect classification system for classifying thetype of the defect detected by means of the defect detection system, andan output unit for generating the defect type information that has beenclassified by means of the defect classification system.

Furthermore, in the present invention, a method for inspecting thesurface of a sample comprises a step for epi-illuminating the surface ofthe sample, a step for detecting the reflected light reflected from thesample that is epi-illuminated, a step for slant-illuminating thesurface of the sample, a step for detecting the reflected lightreflected from the sample that is slant-illuminated, a step fordetecting the defect on the sample surface based on the respectivedetected signals of the detected slant illumination reflected light andof the detected epi-illumination reflected light, a step for classifyingthe detected defect, and a step for supplying the classified result.

Furthermore, in the present invention, a method for inspecting thesurface of a sample comprises a step for illuminating a desired regionof the sample from the high angle direction with respect to the surfaceof the sample, a step for detecting the reflected light reflected fromthe desired region of the sample that is illuminated from the high angledirection, a step for illuminating a desired region of the sample fromthe low angle direction with respect to the surface of the sample, astep for detecting the reflected light reflected from the desired regionof the sample that is illuminated from the low angle direction, a stepfor detecting the defect on the desired region of the sample based onthe respective detected signals of detected reflected light arising fromillumination from the high angle direction and of detected reflectedlight arising from illumination from the low angle direction, a step forclassifying the detected defect, and a step for displaying theclassified result on a screen.

Furthermore, in the present invention, a method for inspecting thesurface of a sample comprises a step for illuminating the sample fromthe first angle direction with respect to the surface of the sample andfor detecting the reflected light reflected from the sample, a step forilluminating the sample from the second angle direction with respect tothe surface of the sample and for detecting the reflected lightreflected from the sample, a step for detecting the defect on the samplesurface based on the first detected signal obtained by detecting thedetected reflected light arising from the first angle directionillumination and based on the second detected signal obtained bydetecting the detected reflected light arising from the second angledirection illumination, a step for classifying the detected defect, anda step for supplying the classified result.

According to the above-mentioned structure, the defect is discriminatedbetween the very shallow small scratch and the foreign object that occurwhen the surface of an insulating film or the like of a sample issubjected to CMP process, and further discriminated between the linearlarge scratch and the foreign object. Furthermore, the small scratch isdiscriminated between the tire mark, the dimple mark and the roughsurface. As the result, it is possible to find out the cause of thedefect easily.

These and other objects, features and advantages of the invention willbe apparent from the following more particular description of preferredembodiments of the invention, as illustrated on the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural diagram illustrating the first exampleof a surface inspection apparatus in accordance with the presentinvention.

FIG. 2A and FIG. 2B are diagrams illustrating the configurationparameter of the scratch and foreign object that occur on an insulatingfilm respectively in CMP process or the like in accordance with thepresent invention.

FIG. 3A to FIG. 3D are diagrams illustrating the incident lightprojection length formed when a light flux d is irradiated on a scratchand a foreign object in accordance with the present invention.

FIG. 4 is a diagram for describing a discrimination principle betweenthe scratch and the foreign object in accordance with the presentinvention.

FIG. 5 is a graph for describing a discrimination example between thescratch and the foreign object in accordance with the present invention.

FIG. 6 is a flow chart for describing an example of discriminationprocess flow between the scratch and the foreign object in accordancewith the present invention.

FIG. 7A to FIG. 7D are diagrams illustrating examples of perpendicularirradiation and pseudo perpendicular illumination in accordance with thepresent invention.

FIG. 8 is an explanatory diagram for describing the conventionalepi-illumination technique.

FIG. 9 is a schematic structural diagram illustrating a modified exampledifferent from the first example shown in FIG. 1 in that the modifiedexample involves two direction light receiving.

FIG. 10 is a schematic structural diagram for illustrating the secondexample in which a surface inspection apparatus involves multipledirection light receiving in accordance with the present invention.

FIG. 11A and FIG. 11B are a plan view and a front view of a multipledirection detection optical system respectively shown in FIG. 10.

FIG. 12A to FIG. 12D are diagrams illustrating the second example thatuses the multiple direction detection optical system shown in FIG. 10.

FIG. 13A and FIG. 13B are diagrams illustrating the diffracted lightdistribution diffracted when a linear large scratch is illuminated inaccordance with the present invention.

FIG. 14 is a diagram illustrating the discrimination principle by meansof reception of the light diffracted from the linear large scratch inaccordance with the present invention.

FIG. 15 is a flow chart for describing an example of a discriminationprocess flow for discriminating between a large scratch and a non-lineardefect in accordance with the present invention.

FIG. 16 is a diagram for describing an example of the whole flow of adiscrimination algorithm in accordance with the present invention.

FIG. 17 is a flow chart for describing an example of a discriminationprocess flow for discriminating between a large scratch and a foreignobject in accordance with the present invention.

FIG. 18 is a diagram for describing the diffracted light distributionfor each scratch configuration in accordance with the present invention.

FIG. 19 is a diagram for describing an example of a scratchconfiguration classification process flow in accordance with the presentinvention.

FIG. 20A and FIG. 20B are diagrams for illustrating an example of ascratch configuration classification result in accordance with thepresent invention.

FIG. 21 is a diagram for describing an example of a discriminationresult layout displayed on a display unit in accordance with the presentinvention.

FIG. 22 is a graph for describing an example of a tire mark luminancedistribution in accordance with the present invention.

FIG. 23 is a diagram for describing an example of table calculation dataitems in accordance with the present invention.

FIG. 24 is a schematic structural diagram illustrating the third exampleof a surface inspection apparatus in accordance with the presentinvention.

FIG. 25A and FIG. 25B are diagrams illustrating an example of thediffracted light distribution on the Fourier transformation plane shownin FIG. 24.

FIG. 26 is a flow chart for describing an example of a diffracted lightdistribution evaluation flow on the Fourier transformation plane shownin FIG. 24.

FIG. 27 is a perspective view illustrating an example in which anexample of a surface inspection apparatus in accordance with the presentinvention is applied to a wafer having a wiring pattern.

FIG. 28 is a schematic structural diagram illustrating the fourthexample of a surface inspection apparatus in accordance with the presentinvention.

FIG. 29A and FIG. 29B are diagrams illustrating an example of a behindphase filter shown in FIG. 28.

FIG. 30 is a diagram illustrating an example of an ahead phase filtershown in FIG. 28.

FIG. 31 is an explanatory diagram for describing the phase differencecaused by a scratch and foreign object in accordance with the presentinvention.

FIG. 32 is an explanatory diagram for describing the principle of thephase difference and luminance generation caused by a scratched portionin accordance with the present invention.

FIG. 33 is an explanatory diagram for describing the principle of thephase difference and the luminance generation caused by a foreign objectportion in accordance with the present invention.

FIG. 34 is a discrimination explanatory diagram for discriminatingbetween a scratch and foreign object by means of phase differencetechnique shown in FIG. 28.

FIG. 35 is an enlarged perspective view illustrating a wafer edgeportion.

FIG. 36 is a perspective view illustrating the scattered lightdistribution scattered from the wafer edge portion when epi-illuminationis irradiated.

FIG. 37 is a plan view illustrating the scattered light distributionscattered from a wafer edge portion and defect when epi-illumination isirradiated.

FIG. 38 is an explanatory diagram illustrating an example fordiscrimination processing between a wafer edge portion and defect.

FIG. 39 is an explanatory diagram illustrating another example fordiscrimination processing between a wafer edge portion and defect.

FIG. 40 is a diagram illustrating an example of a space filter used inFIG. 39.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of a surface inspection apparatus and a method for surfaceinspection designed for stable operation of flattening work processemployed in the semiconductor manufacturing process or magnetic headmanufacturing process in accordance with the present invention will bedescribed in detail hereinafter with reference to the drawings.

At first, the first embodiment of a surface inspection apparatus and amethod for surface inspection in accordance with the present inventionwill be described. In detail, in the first embodiment, a scratch 23 ahaving a shallow depth formed on a wafer 10 is discriminated from aforeign object 24 adhered on the wafer 10, which have been formed when aSiO₂ film (a work target) 22 is formed on a Si wafer 21 and subjected toCMP (Chemical Mechanical Polishing) as shown in FIG. 2A and FIG. 2B. Insome cases, there is no Si substrate under the SiO₂ film 22 but there isa wiring layer. In CMP process, the surface of the SiO₂ film 22 ispolished to be flatten. Therefore, a scratch 23 a, namely a grindingflaw, is formed on the surface of the SiO₂ film 22 as shown in FIG. 2A.Herein, the film thickness of the SiO₂ film 22 is denoted by t, thewidth of the scratch 23 is denoted by W, and the depth of the scratch isdenoted by D. W is approximately 0.2 μm to 0.4 μm. D is approximatelyseveral nm to the deepest of 100 nm. As described hereinabove, thescratch 23 a formed in CMP is characterized by very shallow depth withrespect to the width. The size parameter of the foreign object 24 isshown in FIG. 2B. Herein, the foreign object 24 is regarded as aparticle having a diameter φ typically. The actual foreign object 24 isnot spherical as described in FIG. 2B, but it is true that, though thedepth D of the scratch 23 a is very shallower as several nm to severaltens nm than W of the scratch 23 a (approximately 0.2 μm to 0.4 μm), themagnitude of the width of the foreign object 24 is not so different fromthe magnitude of the height of the foreign object 24. In the presentinvention, the characteristic dimension ratio of the scratch 23 a isutilized as the point.

Aside from the dimension ratio, the scratch is shaped variously.Particularly, CMP involves chemical mechanism and mechanical mechanismmixedly. A scratch 23 a that is caused from malfunction of mechanicalpolishing with a very small grinding mechanism is a minute linearscratch. Though it causes seldom, a linear large scratch 23 b having alarge depth with respect to the width is formed. However, a scratch 23 aand a scratch 23 b caused from malfunction of chemical polishing, namelyetching polishing mechanism, is dimple-like V-shaped. As describedhereinabove, the configuration of the scratch 23 is different dependingon the cause of malfunction in polishing. In other words, the detailedclassification of the scratch configuration is helpful to find the causeof malfunction. Particularly, in the case that the large scratch 23 b isformed often due to foreign object or in the case that a huge scratch 23c is formed, the polishing process is shut down immediately and thecountermeasure must be devised.

The first example of a surface inspection apparatus for inspecting thescratch or the like used for realizing the first embodiment will bedescribed with reference to FIG. 1 to FIG. 9. In detail, as shown inFIG. 1, the surface inspection apparatus of the first example isprovided with a wafer 10 that is an object to be inspected placed on astage 15 controllably moved in X-Y direction based on the measuredpositional coordinate, an illumination optical system 1 a comprising alight source 2 having a light source for emitting a light such as Arlaser of wavelength 488 nm (blue wavelength), nitrogen laser, He—Cdlaser, or excimer laser (not limited to a laser light source), anoptical path switching mechanism 3, and reflection mirrors 4 a, 4 b, and4 c, a detection optical system 5 comprising a condenser lens 6 and aphotoelectric converter 7 having a photomultiplier, CCD camera, CCDsensor, or TDI sensor, a computation processing unit B comprising an A/Dconversion unit 16 for converting the analog luminance signal suppliedfrom the photoelectric converter 7 to the digital luminance signal, amemory unit 17 for temporarily storing the digital luminance signalobtained from the A/D conversion unit 16, and a comparison computingunit 18, a stage controller 14 for controlling the running of the stage15 based on the positional coordinate measured by means of the stage 15,and a whole controlling unit 9 for controlling the stage controller 14,for controlling the optical path switching mechanism 3, for controllingthe computation processing unit 8, and for receiving the inspectionresult obtained from the computation processing unit 8.

A light source 2 that emits a light having the short wavelength such asan excimer light source is preferably used to detect discriminatinglybetween very small foreign object 24 and scratch 23 that occur on aninsulating film 22 subjected to CMP. The light emitted from the lightsource 2 is irradiated on the wafer surface (the surface of theinsulating film subjected to CMP) in the normal line direction orapproximately in the normal line direction through the reflection mirror4 a and reflection mirror 4 c without direct irradiation on the surfaceof the condenser lens 6. The above-mentioned irradiation is referred toas epi-illumination 12. Otherwise, the light is irradiated on the wafersurface (the surface of the insulating film subjected to CMP) in theslant direction through the reflection mirror 4 b by withdrawing thereflection mirror 4 a by means of the optical path switching mechanism3. The irradiation is referred to as slant illumination 11.

In the first example, one light source 2, a plurality of reflectionmirrors 4 a to 4 c, and an optical path switching mechanism 3 are usedto realize the epi-illumination and slant illumination, but independenttwo light sources may be used respectively. The number of reflectionmirrors and use of the optical path switching mechanism are optional.Any illumination optical system 1 a may be used as long as twoilluminations irradiated on the CMP surface subjected to CMP of theinsulating film 22 on the wafer 10 in the normal line direction orapproximately in the normal line direction and in the slant direction(an angle of approximately 30 degrees or smaller) near the horizontalsurface of the wafer respectively are realized.

Next, the detection sequence will be described. The detection isperformed twice with switching of the illumination direction on onewafer. In detail, at first, the epi-illumination light 12 is irradiatedonto the CMP surface of the insulating film 22 on the wafer 10 withoutdirect irradiation on the surface of the condenser lens 6. As theresult, only the scattered light (low order diffracted light component)emitted from the very shallow small scratch 23 a and the foreign object24 that occur due to CMP on the insulating film 22 is converged on thelight receiving plane of the photoelectric converter 7 comprising theCCD or TDI sensor by means of the condenser lens 6 in the state that theregular reflected light component generated from the insulating film 22is removed without generation of stray light reflected from the roughsurface on the condenser lens and very small foreign objects adhered onthe surface of the condenser lens 6. The output of the photoelectricconverter 7 is subjected to A/D conversion by means of the A/Dconversion unit 16 to obtain the luminance value S(i) for each defect i,and then written in the memory unit 17 temporarily.

Next, the whole controlling unit 9 controls the stage 15 to therebyswitch the irradiation direction by use of the optical path switchingmechanism 2, and as the result the same coordinate position on the wafersurface is irradiated with the slant illumination 11. As the result,only the scattered light (low order diffracted light component) emittedfrom the very shallow small scratch 23 a and the foreign object 24 thatoccur on the insulating film 22 due to CMP is converged on thephotoelectric converter 7 by means of the condenser lens 6 in the statethat the regular reflected light component generated from the insulatingfilm 22 is removed. Then, the output of the photoelectric converter 7 isA/D-converted by means of the A/D conversion unit 16 to obtain theluminance value T(i) for each defect i, and the luminance value T(i) isstored in the memory unit 17 temporarily.

Next, the comparison computing unit 18 calculates the ratio R(i) of thedetected luminance value S(i) for each defect i that has been alreadyobtained during the epi-illumination 12 stored in the memory unit 17 tothe detected luminance value T(i) for each defect i that has beenobtained during the slant illumination. If the calculated luminanceratio R(i) is larger than the previously set threshold value (thereference value for determination: the discrimination line 20 shown inFIG. 5), then the comparison computing unit 18 discriminates it to be aforeign object 24, on the other hand if the luminance ratio R(i) issmaller than the threshold value, then the comparison computing unit 18discriminates it to be a very shallow small scratch 23, and thecomparison computing unit 18 supplies the result to the whole controlunit 9. As described hereinabove, because a scratch 23 a formed when CMPis applied is very shallow and small, the feeble stray light generatedfrom the surface of the condenser lens 6 when the epi-illumination light12 is irradiated on the surface of the condenser lens 6 prevents thediscrimination of the scattered light emitted from the scratch 23 a ifthe stray light is received by the photoelectric converter 7. To avoidsuch problem, the apparatus is structured so that the epi-illuminationlight 12 is not irradiated on the surface of the condenser lens 6.

In the first example of the present embodiment, the epi-illumination 12is used for detection at first and the slant illumination 11 is used fordetection at second, but the slant illumination may be used at firstbefore the epi-illumination 12 is used for detection. In the structureshown in FIG. 1, the case in which the optical path of the laser emittedfrom the laser light source 2 is switched by use of the reflectionmirror 4 a for switching between the epi-illumination and the slantillumination is described, but the case in which a light source forepi-illumination and a light source for slant illumination are providedseparately may be employed. Otherwise, the case in which the wavelengthof the light emitted from an epi-illumination light source isdifferentiated from the wavelength of the light emitted from a slantillumination light source and the reflected lights having the respectivedifferent wavelengths are detected separately for the epi-illuminationand the slant illumination to thereby detect the reflected light of theepi-illumination and the reflected light of the slant illuminationsimultaneously and separately may be employed.

In the first example of the present embodiment, the case in which thedetected luminance value T(i) of the slant illumination 11, namely theluminance value corresponding to the second detection, is A/D convertedand then written in the memory unit 17 temporarily is describedhereinabove, but the case in which the comparison computing unit 18refers to the detected luminance value S(i) of the epi-illumination 12that has been stored already, namely the luminance value correspondingto the first detection, at the time when the detected luminance valueT(i) for the second detection is detected to thereby compute theluminance comparison ratio without storing the second detected luminancevalue T(i) may be employed to realize the present invention.

Next, the discrimination principle involved to realize theabove-mentioned embodiment in accordance with the present invention willbe described in detail herein under with reference to FIG. 3A to FIG. 3Dand FIG. 4. In the present invention, the light flux d is irradiated onone defect in two different directions (for example, epi-illumination 12and slant illumination 11) for discrimination of the defect. At first,the defect is irradiated with the light flux d in the normal linedirection of the wafer surface or approximately in the normal linedirection, namely epi-illumination light 12, without direct irradiationon the surface of the condenser lens 6. Next, the defect is irradiatedwith the light flux d with an angle approximately in the horizontaldirection with respect to the wafer surface, namely slant illuminationlight 11.

The order of the epi-illumination and the slant illumination may bearbitrary. The defect is discriminated by comparing the intensity ofscattered lights emitted from the defect 23 a or 24 obtained when thelight flux d is irradiated in two directions. The intensity of thescattered light from the defect 23 a or 24 depends on the light sourcequantity received by the defect 23 a or 24. As shown in FIG. 3A to FIG.D, the light source quantity received by the defect 23 a or 24 isapproximately proportional to the projected area of the defect in thelight source incident direction. In the case of the scratch 23 a, theprojected area is dependent on the width W for epi-illumination, and theprojected area is proportional to D′ for the slant illumination. Becausethe value of the depth D of the scratch is smaller than the value of thewidth W, the slant illumination projected length D′ is extremely smallerthan the epi-illumination projected length W′. Therefore, the lightsource quantity received by the scratch 23 a for the slant illumination11 is smaller than that for the epi-illumination, and as the result thelight quantity of the scattered light emitted from the scratch for theslant illumination 11 is smaller than that for the epi-illumination. Onthe other hand, in the case of the foreign object 24, because therespective projected lengths φ of the slant illumination and theepi-illumination are approximately equal, the light quantity of thescattered light emitted from the foreign object 24 for the slantillumination is almost equal to that for the epi-illumination.Therefore, as shown in FIG. 4, the detected luminance value of thescattered light for the epi-illumination 12 is compared with that forthe slant illumination, and if the detected luminance value for theslant illumination 11 is smaller than that for the epi-illumination 12,then the defect is discriminated to be a scratch 23 a, and if thedetected luminance value for the slant illumination 11 is equal to orlarger than that for epi-illumination, then the defect is discriminatedto be a foreign object 24.

Aside from the above, because the insulating film (for example, SiO₂film) 22 on which the scratch 23 a is formed due to CMP is transparentwith respect to the light, the regular reflected light is reflected fromthe bottom layer including light interference. Particularly in the caseof epi-illumination, it is required that the regular reflected light(including light interferential light) from the surface and the bottomlayer of the insulating film 22 is guided to the outside of the visualfield of the condenser lens 6 so as not to be detected. As a matter ofcourse, also in the case of the slant illumination 11, it is requiredthat the regular reflected light (including interferential light) isguided to the outside of the visual field of the condenser lens 6 so asnot to be detected. In the case that a light source for emitting broadband light or white light is used, the problem arising from the lightinterference between the regular reflected light from the surface of theinsulating film 22 and the regular reflected light from the bottom layeris avoided. However, UV light or DUV light is preferably used as theillumination light to obtain the strong scattered light from a small(particularly the depth D is very shallow) scratch 23 a or a foreignobject 24 on the insulating film 22.

An example of the discrimination result is shown in FIG. 5 graphically.In the graph, the abscissa represents the detected luminance value forthe epi-illumination and the ordinate represents the detected luminancevalue for the slant illumination. In this case, the region under thediscrimination line 20 is the region of the scratch 23 and the regionabove the discrimination line 20 is the region of the foreign 24 in thedrawing.

Next, an example of the flow for computation processing by means of theabove-mentioned discrimination method will be described with referenceto FIG. 6. At first, in step S61, the photoelectric converter 7 detectsthe luminance signal S(i) for each defect i for the epi-illumination 12and A/D converts the detected signal, and stores the converted signal inthe memory unit 17. Next, in step S62, the photoelectric converter 7detects the luminance signal T(i) for each defect i for the slantillumination 11 and A/D converts the detected signal, and stores theconverted signal in the memory unit 17. Then, in step S63, thecomparison computing unit 18 calculates the ratio R(i) of the luminancesignal T(i) for each defect i detected for the slant illumination to theluminance signal S(i) for each defect i detected for theepi-illumination stored in the memory unit 17 according to the equation1 described herein under.R(i)=T(i)/S(i)  (equation 1)

Herein, i denotes the identification number given to each defect toevaluate a plurality of defects. Because one defect can be detected as aplurality of defects depending on the size of the light flux d and thephotoelectric converter 7 pixel size in some cases, it is required thatsignals that indicate defects located closely each other are subjectedto expansion processing (concatenate processing) so as to be convertedto a single signal that indicates one defect. Therefore, theidentification number i given to each defect is given to a signal thatindicates one defect that has been subjected to concatenate processing.

Furthermore, in step S64, the comparison computing unit 18 discriminatesthe defect to be a foreign object 24 if the luminance ratio R(i)calculated as described hereinabove is larger than the previously setthreshold value (the reference value for determination: thediscrimination line 20 shown in FIG. 5), on the other hand thecomparison computing unit 18 discriminates the defect to be a scratch 23a if the luminance ratio R(i) is smaller than the threshold value, andthe result is supplied to the whole control unit 9. The case in whichthe detected luminance value T(i) for the slant illumination is dividedby the detected luminance value S(i) for the epi-illumination isdescribed in the present example, but the case in which the detectedluminance value S(i) for epi-illumination is divided by the detectedluminance value T(i) for the slant illumination may be employed. In thiscase, if the ratio R(i) is larger than the previously set thresholdvalue (the reference value for determination: the discrimination line 20shown in FIG. 5), then the defect is discriminated to be a scratch 23 a,and on the other hand if the ratio R(i) is smaller than the thresholdvalue, then the defect is discriminated to be a foreign object 24.

Next, an example of the location method of the reflection mirror 4 cwill be described with reference to FIG. 7A to FIG. 7D. The purpose ofthe method is to prevent the stray light of the dark field detectionsystem and to detect the defect at high sensitivity. The illumination inthe direction near the normal line with respect to the plane of thewafer 10 is required for inspection of a scratch 23 a as it is obviousfrom the principle described hereinbefore.

However, in the case of the illumination method (the reflection mirror 4c′ is located above the lens 6) as shown in FIG. 8, the incident lightpasses through the condenser lens 6 and is irradiated onto the wafer 10.As the result, the stray light is generated to cause noise on thedetected image. In detail, small polishing marks on the surface of thecondenser lens 6 and dusts adhered on the condenser lens 6 causescattered light, and the scattered light behaves as the stray light.Because of the above, when a feeble scatted light emitted from thedefect 23 a or 24 is received by the photoelectric converter 7 forobservation, the stray light definitely prevents the observation. Inother words, the scattered light emitted from a minute scratch 23 acannot be detected discriminatingly from the stray light.

To avoid such problem, in the present invention as shown in FIG. 7A andFIG. 7B, the reflection mirror 4 c is located so that the incident lighthaving high intensity is not irradiated onto the surface of thecondenser lens 6, and the zero order diffracted light, namely theregular reflected light component reflected from the wafer 10 (thesurface of the interlayer insulating film (CMP plane), the surface ofunder-layered wiring layer, the surface of the scratch 23 a, and thesurface of the foreign object 24, is not irradiated onto the pupil ofthe condenser lens 6, namely in the NA.

FIG. 7A showed a method in which the reflection mirror 4 c 1 is locatedapproximately on the normal line of the wafer 10 between the wafer 10and lens 6, the epi-illumination light 12 a is incident to thereflection mirror 4 c 1 from the horizontal direction so that theepi-illumination light 12 a is not irradiated on the surface of thecondenser lens 6 for reflection, and the regular reflected lightcomponent reflected from the wafer 10 is reflected on the reflectionmirror 4 c 1 so as not to be incident in the pupil of the lens 6, on theother hand only the scattered light (low order diffracted lightcomponent) in the region shaded with slant lines (ring-band shaped inthe plane) out of the scattered light (first or higher order diffractedlight component) emitted from the scratch 23 a or the foreign object 24is incident in the pupil of the lens 6. The shape of the reflectionmirror 4 c 1 is approximately elliptical. The above-mentioned detectionis referred to as the scattered light detection with perpendicularillumination.

Furthermore, FIG. 7B shows a method in which the reflection mirror 4 c 2is located between the wafer 10 and the condenser lens 6 outside the NAof the condenser lens 6 and the epi-illumination light 12 b is incidentto the reflection mirror 4 c 2 from the horizontal direction so as notto be irradiated on the surface of the condenser lens 6 for reflection,and the regular reflected light component reflected from the wafer 10 isincident outside the pupil of the condenser lens 6, and on the otherhand only the scattered light in the region shaded with slant lines outof the scattered light emitted from the scratch 23 a or the foreignobject 24 is incident in the pupil of the lens 6. In the case that thereflection mirror 4 c 2 is expanded in the circumferential direction,the illumination light irradiated by the reflection mirror 4 c 2 is aring-band illumination. However, as shown in FIG. 7B, if the reflectionmirror 4 c 2 is limited partially, the illumination light becomes apartial illumination in the ring-band illumination. Such detection isreferred to as the scattered light detection with pseudo perpendicularillumination.

FIG. 7C shows a method in which the reflection mirror or a half mirror 4c 3 is located above the condenser lens 6 having an aperture 50 at thecenter thereof, the perpendicular illumination light 12 a reflected onthe half mirror 4 c 3 is not irradiated on the surface of the condenserlens 6 but passes through the aperture 50 so as to be irradiated on theCMP surface of the insulating film on the wafer 10, the regularreflected light component reflected on the wafer 10 is shaded by use ofa space filter 51 located on the Fourier transformation plane, and thescattered light obtained through the condenser lens 6 out of thescattered light emitted from the scratch 23 a or the foreign object 24is received by the photoelectric converter 7.

Furthermore, FIG. 7D shows a method in which the epi-illumination light12 a passes through a half mirror 52, passes through an aperture 50 ofthe condenser lens 6, and is irradiated on the CMP surface of the wafer10, the regular reflected light reflected on the wafer 10 is shaded byuse of a space filter 53 located on the Fourier transformation plane,and only the scattered light obtained through the condenser lens 6 outof the scattered light emitted from the scratch 23 a or the foreignobject 24 is reflected by the half mirror 52 and received by thephotoelectric converter 7 in the same manner as used in the method shownin FIG. 7C.

As described hereinabove, in the case of the method described referringto FIG. 7C and FIG. 7D, the aperture 50 is formed at the center of thecondenser lens 6 so that the perpendicular illumination and thescattered light detection in the perpendicular direction are madepossible as in the case of FIG. 7A without generation of the stray lightfrom the surface of the condenser lens 6. Therefore, the scattered lightemitted from the edge of a very shallow scratch 23 a can be receivedrelatively evenly by the photoelectric converter regardless of thedirection of the scratch 23 a in the horizontal plane, and the evendetected luminance value is obtained. Furthermore, as shown in FIG. 13B,the perpendicular illumination is more preferable than the pseudoperpendicular illumination to obtain the diffracted light that isstrongly directional in the right angle direction with respect to thelarge scratch 23 b, namely a linear pattern.

Aside from the above, in the case of the scattered light detection withperpendicular illumination shown in FIG. 7A, the incident light passesunder the lens 6 and will not be irradiated on the surface of thecondenser lens 6 apparently, and the stray light will not be generated.Furthermore, because the regular reflected light reflected on the wafer10 is reflected on the reflection mirror 4 c 1, the regular reflectedlight will not be irradiated in the pupil of the condenser lens 6.Furthermore, it is true for the perpendicular illumination shown in FIG.7C and FIG. 7D. Furthermore, also in the case of the scattered lightdetection with pseudo perpendicular illumination, the incident lightwill not pass the condenser lens 6 apparently. Because the reflectionmirror 4 c 2 is located outside the NA of the condenser lens 6, theregular reflected light component reflected on the wafer 10 is notirradiated in the pupil of the condenser lens 6. As describedhereinabove, in any method, the epi-illumination is realized so that theincident light that has a strong light intensity and is apt to generatethe stray light is not irradiated on the surface of the condenser lens6, and the regular reflected light reflected from the wafer is notincident to the condenser lens 6. Therefore, the stray light is notgenerated and it is possible to obtain the detected image having highS/N ratio from the scratch 23 a and the foreign object 24 that occur onthe CMP surface of the interlayer insulating film 22 subjected to CMP.Because the interlayer insulating film 22 is transparent with respect tothe light, the light regularly reflected on the bottom layer returnsfrom the bottom layer when the epi-illumination is irradiated. However,because the regularly reflected light is not irradiated in the NA of thelens 6 as described herein under, the regular reflected light does notadversely affect the detection of the scattered light emitted from thescratch 23 a and the foreign object 4, and it is possible to detect thescratch 23 a and the foreign object 24 by mean of the signal obtainedfrom the photoelectric converter 7.

Furthermore, using of the epi-illustration 12 a and 12 b together withthe slant illumination 11 improves the detection sensitivity incomparison with the case in which only the slant illumination 11 isused, because the strong light component of the scattered lightintensity distribution from the scratch 23 a is easily received inaddition to the reason of solution of the stray light problem. Thereason is that the low order diffracted light component out of thescattered light intensity from the scratch 23 a is relatively strong. Inother words, by irradiating the light approximately in the normal linedirection with respect to the wafer plane, the low order diffractedlight is reflected from the wafer 10 and easily converged by thecondenser lens 6.

As the result, it is possible to detect the scratch 23 a with highersensitivity in comparison with the case in which only the slantillumination 11 is used. As described hereinabove, it is possible torealize the high sensitivity detection of the scratch 23 a by using onlythe perpendicular illumination 12 a or the pseudo perpendicularillumination 12 b.

In the case that the reflection mirror 4 c 1 is located in the NA of thecondenser lens 6, by forming the shape of the reflection mirror 4 c 1approximately elliptical so as not to affect adversely the image formingcharacteristic of the lens 6, the scattered light in the region shadedwith slant lines (the ring-band region in the plane) shown in FIG. 7A isconverged by the condenser lens 6 to form an image. However, in the casethat the reflection mirror 4 c 1 located in the NA of the condenser lens6 adversely affects the image-forming characteristic, a mechanism thatis served to withdraw the reflection mirror 4 c 1 outside the NA whenthe perpendicular illumination is irradiated is required. It is requiredthat dust generated from the defect inspection apparatus is reduced tothe extremely low level in the semiconductor inspection. From this viewpoint, it is not preferable that the movable mechanism is located abovethe wafer. However, in such case, the pseudo perpendicular illumination12 b may be used. In the case of the pseudo perpendicular illumination12 b, the reflection mirror 4 c 2 will not adversely affect the imageforming characteristic because the reflection mirror 4 c 2 is locatedoutside the NA, and it is not required that a withdrawing mechanism isprovided separately.

Furthermore, in the case that a surface inspection apparatus forinspecting the scratch in accordance with the present invention is usedas a foreign object inspection apparatus with only the slantillumination, the perpendicular illumination is not necessary.Therefore, it is possible that the reflection mirror 4 c 1 shown in FIG.7A is withdrawn so that the entire NA of the condenser lens 6 is used,and the scattered light emitted from the foreign object is effectivelyconverged and received by the photoelectric converter 7.

However, to reduce the generation of dust without withdrawal of thereflection mirror 4 c 1, the pseudo perpendicular illumination 12 b maybe used as the perpendicular illumination of the surface inspectionapparatus though the scratch detection accuracy level is slightlylowered. Furthermore, in the case that the method shown in FIG. 7C andFIG. 7D is used as the perpendicular illumination, the surfaceinspection apparatus can be used as the foreign inspection apparatuswith only the slant illumination without using the perpendicularillumination. In the case that the surface inspection apparatus is usedas the foreign object inspection apparatus with only the slantillumination, because it is required to shade the diffracted patternbased on the diffracted light from the periodical wiring pattern whenthe foreign object on a memory cell, on which the periodical wiringpattern has been formed, is to be detected, the space filters 51 and 53may be replaced with liner space filters.

The case in which one detection optical system 5 is used is described inthe first example of the present embodiment, but the case in which aplurality of detection optical systems 5 a and 5 b are used as shown inFIG. 9 may be employed. Particularly, the detection optical systems 5 aand 5 b are located in the direction that is suitable for detecting thestrongest scattered light emitted from the defect 23 a or 24 for eachirradiation direction to realize the detection at higher sensitivity.For example, as shown in FIG. 9, a lens 6 a and photoelectric converter7 a of the detection optical system 5 a for epi-illumination areprovided in the wafer normal line direction, in which direction thescattered light intensity is very strong. The location of the lens 6 ais applicable to the perpendicular illumination 12 a and the pseudoperpendicular illumination 12 b.

As the detection optical system 5 b for the slant illumination, acondenser lens 6 b and a photoelectric converter 7 b are provided in theregular reflection direction of the slant incident light, in whichdirection the scattered light intensity is very strong. However, as forthe detection optical system 5 b comprising the lens 6 b and thephotoelectric converter 7 b, it is required not to converge the regularreflected light component reflected from the wafer 10. Therefore, it isnot preferable that the detection optical system 6 b is provided in theregular reflected light emergent direction 55, but it is preferable thatthe detection optical system 6 b is located at the place so that theregular reflected light component is irradiated outside the NA of thecondenser lens 6 b. In the case of the present example, because twodetection optical systems 5 a and 5 b are provided, two A/D conversionunits 16 a and 16 b and two luminance memory units 17 a and 17 b areprovided. As a matter of course, one memory unit 17, for example oneRAM, may be used by storing the data separately in the differentaddresses in the memory unit 17.

In the structure shown in FIG. 9, a light source for theepi-illumination and a light source for the slant illumination may beprovided separately. Furthermore, the wavelength of the light emittedfrom the light source for the epi-illumination may be differentiatedfrom that for the slant illumination, the reflected light from the wafersurface is detected separately for respective wavelengths. As theresult, the epi-illumination and the slant illumination are irradiatedsimultaneously, and the reflected light of the epi-illumination and thereflected light of the slant illumination are detected simultaneouslyand separately.

The second example of a surface inspection apparatus for detecting thescratch or the like in accordance with the present invention will bedescribed with reference to FIG. 10 to FIG. 12D. The second example ofthe present embodiment is different from the first example in thedetection optical system 5. In detail, the detection optical system 5 ischaracterized by comprising a high angle detection optical system 5 a, amedium angle detection optical system 5 c, and a low angle detectionoptical system 5 b. The structure for placing the substrate table 51 onwhich a wafer 10, namely an object to be inspected, is fixed by meansof, for example, vacuum-suction on the stage 15 is omitted in the firstexample. In the second example, the stage 15 comprises a linearly movingstage 15 a and a rotationally moving stage 15 b. In other words, anystage 15 may be used as long as a wafer 10 is transferred so that thearbitrary position on the wafer 10 is irradiated with a light.Furthermore, as for the computation processing unit 8, the A/Dconversion unit 16 and the memory unit 17 are structured correspondinglyto the detection optical systems 5 a to 5 c. The illumination opticalsystem 1 a is structured as in the case of the first example. In otherwords, as for the perpendicular illumination, the illumination lightreflected on the reflection mirror 4 a is reflected on the reflectionmirror 4 d, passes through a half mirror 52, passes through an aperture50 formed on a condenser lens 6 a as shown in FIG. 7D, and is irradiatedon the CMP surface of the wafer 10 as the light flux d. The regularreflected light generated from the wafer 10 is shaded with a spacefilter 53, the low order diffracted light emitted from the edge of ascratch 23 a and a foreign object 24 is converged by a condenser lens 6a of the high angle detection optical system 5 a. The convergeddiffracted light is received by a photoelectric converter 7 a, and thehigher order diffracted light is detected by the medium angle detectionoptical system 5 c. As a matter of course, the perpendicularillumination 12 having the structure shown in FIG. 7A, FIG. 7B, or FIG.7C may be used. The slant illumination 11 is reflected on the reflectionmirror 4 b and irradiated on the CMP surface of the wafer 10 as thelight flux d. The regular reflected light generated from the wafer 10 isnot detected, but the diffracted light emitted particularly from theforeign object 24 is detected by the detection optical systems 5 a to 5c.

Next, the detection optical system of the second example will bedescribed in detail with reference to FIG. 11A and FIG. 11B. In detail,the detection optical system comprises one high angle detection opticalsystem 5 a, four medium angle detection optical systems 5 c, and fourlow angle detection optical systems 5 b including condenser lenses 6 ato 6 i and photoelectric converters 7 a to 7 i. Photomultipliers areused as the photoelectric converters 7 a to 7 i in the present example.Nine photomultipliers are used and located in the dome arrangement asshown in FIG. 11A and FIG. 11B. The photomultipliers 7 a to 7 i areprovided with condenser lenses 6 a to 6 i respectively. The case inwhich the condenser lenses 6 a to 6 i and the photomultipliers 7 a to 7i are used for the detection optical system is described in the presentexample, but, for example, the case in which CCD camera or TDI sensor isused may be employed to form an image. Furthermore, the number ofphotoelectric converters 7 a to 7 i is by no means limited to 9. Theoutputs of the photoelectric converters 7 a to 7 i are written in thememory units 17 a to 17 i by way of ND conversion units 16 a to 16 i.Simultaneously, the coordinate data of the wafer 10 obtained from thestage controller 14 is written in the memory units 17 a to 17 i. Thecoordinate data and the luminance data are transmitted to a comparisoncomputing unit 18. In the case that the entire surface of the wafer isinspected, it is required to write the coordinate data and the luminancedata in the memory units 17 a to 17 i as described hereinabove. However,in the case that the specified coordinate position is inspected fixedly,the coordinate data is not necessarily required. The coordinate data andthe luminance data are not necessarily stored in the same memory units17 a to 17 b in the form of a pair, and may be stored in differentmemory units. Furthermore, the coordinate is not necessarily stored,but, for example, the identification number given to the detected defectmay be stored instead of the coordinate. Any method may be employed aslong as the detection luminance data for the slant illumination and thedetection luminance data for the epi-illumination of the same defect arecorrelated each other. In the present example, the data of the samecoordinate position or on the position near to the coordinate positionout of the data of two set of the epi-illumination and the slantillumination are recognized as the luminance data of the same defect byusing the coordinate data. Thereby, the luminance value S(i) of theepi-illumination 12 is compared with the luminance value T(i) of theslant illumination 11.

As shown in FIG. 11A and FIG. 11B, one detection optical system 5 a islocated in the incident direction of the epi-illumination 12 (having theangle Av from the normal line direction with respect to the wafer plane.Preferably, the angle Av is 0). This detection optical system 5 a isreferred to as high angle detection optical system 5 a. Four detectionoptical systems 5 c and four detection optical systems 5 b are locatedin the order from the position near the high angle detection opticalsystem 5 a to the position near the wafer plane, and the former isreferred to as the medium angle detection optical system 5 c and thelatter is referred to as the low angle detection optical system 5 b. Thecase in which total nine detection optical systems are used is describedin the present example, but the number of detection optical systems isby no means limited to 9 as the means for realizing the presentinvention.

In the present example, the case in which all the nine detection opticalsystems 5 a to 5 c are used as the light receiving means when theepi-illumination is applied as shown in FIG. 12A and FIG. 12B, and thesum of the received light luminance of the nine photoelectric converters7 a to 7 i is used as the received light luminance when theepi-illumination 12 is applied is described. However, it is notnecessarily required to use all the nine detection optical systems toobtain the received light luminance with the epi-illumination, but onlythe high angle detection optical system 5 a, or only medium angledetection optical system 5 c, or the sum of received light quantity ofthe high angle detection optical system 5 a and the medium detectionoptical system 5 c may be used. Particularly for detection of the loworder diffracted light emitted from the scratch 23 a and foreign object24 with the epi-illumination, only the medium angle detection opticalsystem 5 c may be used instead of the high angle detection opticalsystem 5 a. At that time, because the regular reflected light (zeroorder diffracted light) is not incident on the NA of the medium angledetection optical system, the sum of light quantity of the medium angledetection optical system 5 c may be calculated simply. As describedhereinabove, various combinations may be used selectively, but in thepresent example, the sum of the received light quantity of all thedetection optical systems 5 a to 5 c is used so that the defectdetection sensitivity is maximized, that is, so that so-called high NA(Numerical Aperture) is realized. However, because most of diffractedlight emitted from the scratch 23 a and the foreign object 24 isdetected by means of the high angle detection optical system 5 a and themedium angle detection optical system 5 c, it is preferable to use thesum of the received light quantity of both detection optical systems.

As the light receiving means that is used when the slant illumination 11that makes an angle of Vo with respect to the wafer plane is irradiated,two low angle light receivers 6 b, 7 b: 6 c, 7 c located on the sidenear to the regular reflection direction reflected from the wafer whenthe slant illumination is incident as shown in FIG. 12C and FIG. 12D areused. The sum of the received light luminance of these two receivers isused as the received light luminance obtained when the slantillumination 11 is irradiated. The light receiver to be used is by nomeans limited to the two low angle light receivers. In the presentexample, the detection optical system (condenser lens 6 b andphotoelectric converter 7 b) 5 b that is located in the direction wherethe strong scattered light distribution intensity is detected is merelyselected without receiving the regular reflected light in order torealize high sensitivity detection as described referring to FIG. 9.From the view point of discrimination, it is important that twodirectional illuminations are used and the respective scattered lightintensities are detected, and the direction of the light receiving means5 b is not so important. The direction of the detection optical system(condenser lens 6, and photoelectric converter 7) 5 may be determineddepending on the level of requirement for discriminating between a smallforeign object 24 and scratch 23 a. In the case that the high angledetection optical system 5 a is used as the detection optical system 5,it is required not to generate stray light from the surface due to theepi-illumination.

The example of the method for discriminating between the foreign object24 and the scratch 23 a by use of two directional illuminationsdescribed hereinabove is based on the fact that the depth of the scratch23 a is characteristically shallow.

However, as described hereinabove, in some cases a large foreign objectcomes in a CMP apparatus from the external and causes a very deep flawthough it occurs seldom in the case of CMP. In the case that a largeforeign object comes in during polishing and the large foreign object,not a very small grinding abrasive grain, causes the scratch, a scratch23 b having a large depth with respect to the width W is formed. In thecase of the scratch 23 b having a deep depth as described hereinabove,the scratch is mis-recognized to be a foreign object 24 through it isreally a scratch 23. As the result, the huge scratch that should berecognized is not recognized.

Then, the second embodiment for recognizing discriminatingly between adeep scratch 23 b and a foreign object 24 will be described hereinafter.In the first embodiment, because the ratio R(i)=T(i)/S(i) is large forthe foreign object 24 and also for the deep scratch, the large scratch23 b having deep depth and also the foreign object 24 are detectedtogether in step S64 of the discrimination processing flow shown in FIG.6. Then, the purpose of the second embodiment is to discriminate betweenthe large scratch 23 b and the foreign object 24 correctly. Herein, S(i)denotes the luminance data for each defect after concatenate processingof the first inspection with the epi-illumination 12. T(i) denotes theluminance data at the same coordinate value i out of data for eachdefect after concatenate processing of the second inspection with theslant illumination 11.

The discrimination is based on the fact that the scratch 23 b having adeep depth D with respect to the width W has a long length inherently.The reason is that the wafer is polished with rotation in CMP processand the deep scratch will not have a short length differently from thenick having a local deep concave. The second embodiment of the presentinvention is based on the above-mentioned certainty, a linear longdefect is further classified as the large scratch 23 b out of defectsrecognized as the foreign object 24 in step S64 shown in FIG. 6. At thattime, the defect is classified based on the principle shown in FIG. 13Aand FIG. 13B. When a light flux 12 is irradiated from the normal linedirection onto a large scratch 23 b with linear pattern as shown in FIG.13B, the diffracted light exhibits a distribution having very strongdirectionality in the right angle direction of the linear pattern 23 b.FIG. 13A shows a case in which a light flux 11 is irradiated withinclination from the normal line direction onto the large scratch 23 bhaving a linear pattern, and shows the principle of space filteringmethod for removing the linear diffracted light pattern arising fromwiring patterns repeatedly arranged regularly with irradiation of theslant illumination used in the foreign object inspection apparatus. Inthe present invention, the strong directionality of the diffracted lightemitted from the large scratch 23 b with irradiation of theperpendicular illumination 12 is recognized as shown in FIG. 13B.Thereby, the defect is recognized as a large scratch 23 b having alinear pattern and not the foreign object 24.

The discrimination principle between the large scratch 23 b and theforeign object 24 will be described with reference to FIG. 14 and FIG.15. At first, for example, the epi-illumination 12 is applied onto thewafer 10, and the computation processing unit 8 selects the detectionoptical system A having the highest luminance from among a plurality(eight) of low angle and medium angle detection optical systems 5 b and5 c (photoelectric converters 7 b to 7 i) in step S65. Next, thecomputation processing unit 8 refers to the luminance value Sb(i) of thedetection optical system B that is orthogonal to the A detection opticalsystem in step S66, and compares the luminance value Sa(i) of thedetection optical system A with the luminance value Sb(i) of thedetection optical system B to thereby calculate the luminance ratio(Sa(i)/Sb(i)) in step S67. Next, the computation processing unit 8compares the calculated luminance ratio (Sa(i)/Sb(i)) with thepreviously set value (threshold value), and classifies the luminanceratio larger than the threshold value as a large scratch 23 b, namelylinear defect, and the luminance ratio smaller than the threshold valueas a foreign object 24, namely non-linear defect, or a small scratch 23a.

As described hereinabove, according to the second embodiment, becausethe computation processing unit 8 discriminates the large scratch 23 bfrom the foreign object 24 or the small scratch 23 a, the combination ofthe first embodiment and the second embodiment is capable ofdiscriminating between the small scratch 23 a, foreign object 24, andlarge scratch 23 b.

Next, the third embodiment used to discriminatingly recognize the deepscratch 23 b from the foreign object 24 will be described hereinafter.In detail, in the third embodiment, the mechanism for extracting thelong huge scratch 23 c, for example, a huge scratch 23 c that extendsacross a wafer, is incorporated as shown in FIG. 16. The long and hugescratch 23 c that can be found visually can be extracted easily only byevaluating the length after concatenate processing by means of thecomputation processing unit 8. However, the function of the presentinvention will not be adversely affected without the processing forextracting the huge scratch 23 c.

At first, in the algorithm in the computation processing unit 8, eachinspection data for two incident directions (first inspection:epi-illumination 12, second inspection: slant illumination) is subjectedto concatenate processing in steps S70 a and S70 b to thereby obtain thehuge scratch coordinate data 1 and 2 in steps S71 a and S71 b. Theconcatenate processing involves the expansion processing for recognizingthe data arising from positions located closely each other as the dataof one defect. For example, if signals that indicate defects around thepixel are detected in 3×3 pixels, then the expansion processing forgiving a signal that indicates to the center pixel is repeated aplurality of times to thereby concatenate defects that are locatedclosely each other. One defect can be extracted as a plurality ofdefects erroneously due to the spot size and pixel size unless theconcatenate processing is introduced. Next, the computation processingunit 8 refers to the coordinate data 1 and 2 that indicate the defectafter concatenate processing (for example, refers to the logical sum ofthe signal that indicates the defect) in step S72 to thereby extract along defect as a huge scratch 23 c (prepare the huge scratch data).Furthermore, the computation processing unit 8 refers to the number ofthe coordinate data 1 and 2 that indicate defects concatenated in theconcatenate processing in step S72 to thereby extract a defect having alarge area as a huge scratch 23 c (prepare the huge scratch data).

Next, the computation processing unit 8 removes the data that isrecognized as the data of the huge scratch from each of the firstinspection data and the second inspection data in steps S73 a and S73 brespectively to thereby obtain the concatenated first inspection dataand second inspection data in steps S61 and S62 respectively, and theobtained data is stored in the memory unit 17.

Next, the comparison computing unit 18 discriminates between the scratch23 a and the foreign object 24 or large scratch 23 b with twodirectional illustrations shown in FIG. 6 in step S64 by use of theconcatenated first inspection and second inspection data obtained andstored in the memory unit 17.

Next, the computation processing unit 8 discriminates the data of thelarge scratch 23 b from the data discriminated as the data of theforeign object 24 or large scratch 23 b in steps S65 to S68 as shown inFIG. 15. This discrimination processing will be described in detail withreference to FIG. 17. Eight photomultipliers 7 b to 7 i of the low angledetection optical system 5 b and medium angle detection optical system 5c are used in the discrimination processing. In this case, the solidangle of the low angle is different from that of the medium angle, andthe solid angle difference results in the sensitivity difference betweenthe low angle and the medium angle. The product characteristic of thephotomultipliers 7 b to 7 i is often different individually. Therefore,the sensitivity balance between eight photomultipliers must be adjusted.To adjust the balance, the applied voltage on the each ofphotomultipliers 7 b to 7 i is changed previously to adjust thesensitivity. For very fine sensitivity balance adjustment, it iseffective that the gain is set to each of the photomultipliers 7 b to 7i and the detected luminance is compensated by means of software orhardware. However, the intensity compensation by means of gain is needednot necessarily. Next, the computation processing unit 8 sums up theluminance obtained from the opposite photomultipliers by use of the datathat has been subjected to compensation of sensitivity balance betweenthe photomultipliers in step S75. As the result, eight data of thephotomultipliers 7 b to 7 i are reduced to four data. The computationprocessing unit 8 selects the largest data (ΣSa(i)) from among the fourluminance sum data in step S65 in the same manner as used in step S65shown in FIG. 15. Then, the computation processing unit 8 calculates theorthogonal luminance ratio (ΣSa(i)/ΣSb(i)) with referring to theluminance sum data Sb(i) located at the orthogonal position in steps S66to S67 in the same manner as used in steps 66 and S67. Furthermore, thecomputation processing unit 8 classifies the defect as the large scratch23 b if the orthogonal luminance ratio (ΣSa(i)/ΣSb(i)) is larger thanthe set threshold value 50, and on the other hand classifies the defectas the foreign object 24 if the orthogonal luminance ratio is smallerthan the set threshold value 50 in step S68. By applying the methoddescribed hereinabove, it is possible to discriminate the large scratch23 b, which is apt to be mis-recognized as a foreign object, from theforeign object 24.

Next, the fourth embodiment used to further classify the defect 23 athat has been discriminated as the scratch by means of two directionalilluminations according to configuration will be described in detailhereinafter with reference to FIG. 18 to FIG. 20B. CMP process involvesnot only the mechanical polishing but also chemical polishing such asetching simultaneously. Therefore, CMP is called as chemical mechanicalpolishing. Usually, the mechanical polishing action is predominant inthe oxide film polishing process, and a typical scratch 23 a is acontinuous flaw 23 aa comprising small linear scratches, each of whichis crescent described as tire mark in FIG. 18. On the other hand, whenthe chemical polishing action is predominant, the V-shaped flaw 23 abhaving the circular plane cross section described as dimple mark in FIG.18 is formed often. Furthermore, when a polishing pad that has been usedfor long time and has become hard is used, crowded small scratches 23 acthat is formed in random direction described as rough surface in FIG. 18is caused often. As described hereinabove, the configuration of scratchis various depending on the malfunction cause of polishing condition. Inother words, by recognizing the scratch configuration with breakdownclassification, it is easy to find out the process condition to beimproved, and the time required for malfunction countermeasure issignificantly shortened. Then, the data discriminated as the scratch 23a in the process for discrimination between the foreign object and thescratch by means of two directional illuminations described hereinaboveis classified for configurational breakdown. The scattered lightintensity distribution in the horizontal direction and the verticaldirection is checked in detail to perform configurational classificationof the scratch as shown in FIG. 18. As shown in FIG. 18, because thetire mark 23 aa is a linear mark as described in the large scratchdiscrimination, the tire mark 23 aa causes the diffracted light havingstrong directionality in the horizontal direction. On the other hand,the dimple mark 23 ab and the rough surface 23 ac do not exhibit thedirectionality in the horizontal direction scattered light intensitydistribution. Then, the dimple mark 23 ab is discriminated from therough surface 23 ac by use of the vertical direction scattered lightintensity distribution. The discrimination is based on the fact that thedimple mark 23 ab exhibits the directionality in the vertical directionbut the rough surface does not exhibits the directionality in thevertical direction. To discriminate, the computation processing unit 8evaluates the diffracted light distribution in the horizontal directionor the vertical direction to thereby classify the defect according todetailed configuration as shown in FIG. 19. The case in which bothhorizontal and vertical scattered light intensity distributions are usedis described in the present example, but the case in which any one ofthese distributions is used may be employed depending on theconfiguration to be classified.

In detail, in steps S61 and S62, the first inspection involves the upperdetection (high angle detection optical system 5 a, medium angledetection optical system 5 c, and low angle detection optical system 5b) with the epi-illumination 12, and the second inspection involves thefront low angle detection optical system 5 b (6 b, 7 b; 6 c, 7 c) orhigh angle detection optical system 5 a and/or medium angle detectionoptical system 5 c with slant illumination 11.

Next, in the present example, the computation processing unit 8evaluates the horizontal scattered light intensity distribution(Sha(i)/Shb(i)) with the epi-illumination 12 among the data classifiedas the scratch 23 a in steps S63 and S64 in the same manner as used inthe method shown in FIG. 17 in step S76 at first, and then classifiedthe data having strong directionality as the tire mark 23 aa. Then, thecomputation processing unit 8 evaluates the vertical directionality instep S77 to thereby classify the defect into the dimple mark 23 ab andthe rough surface 23 ac. In the present example, the horizontaldirectionality is checked in the same manner as used in the flow shownin FIG. 17. Various methods have been known for evaluation of verticaldirectionality. For example, the ratio of the detected luminance Sh(i)detected by means of the photoelectric converter 7 a of the high angledetection optical system 5 a to the sum of the detected luminance ΣSI(i)detected by means of photoelectric converters 7 a to 7 i of the lowangle detection optical system 5 b and medium angle detection opticalsystem 5 c (Sh(I)/ΣSI(i) may be calculated. An example of thediscrimination result is shown in FIG. 20A and FIG. 20B. FIG. 20A showsthe result of evaluation of the horizontal luminance ratio(Sha(i)/Shb(i)) with the epi-illumination 12 to classify into the groupof the tire mark 23 aa and the dimple mark 23 ab or the group of therough surface 23 ac, and the FIG. 20B shows the result of evaluation ofthe vertical luminance ratio (Sh(i)/ΣSI(i)) with the epi-illumination 12to classify into the group of the rough surface 23 ac and the group ofthe dimple mark 23 ab. In the FIG. 20B, the directionality of thevertical diffracted light of the dimple mark 23 ab becomes stronger withincreasing of the diameter. This phenomenon agrees with the well-knownprinciple of Airy disk. It is possible to estimate the diameter of adimple mark based on the luminance ratio.

According to the fourth embodiment described hereinabove, it is possibleto discriminatingly inspect the foreign object 24 and the scratch 23having various configuration on the insulating film flattened by meansof CMP process, and the computation processing unit 8 supplies theresult to the memory unit 31 connected to the whole control unit 9, andthe memory unit 31 stores the result.

Next, the fifth embodiment in accordance with the present invention forpreviously evaluating whether the defect is classified correctly or notin the above-mentioned surface inspection of the scratch and the likewill be described with reference to FIG. 1 and FIG. 21 to FIG. 23. Asshown in FIG. 1, the surface inspection apparatus for inspecting thescratch or the like is provided with the memory unit 31, the input means32 comprising a key board, a mouse, and a memory medium, the displayunit 33 comprising a display or the like, and the whole control unit 9connected to the network 34 connected to, for example, a SEM apparatus.As a matter of course, the memory unit 31 stores the inspection resultthat has been discriminatingly processed in the computation processingunit 8.

Furthermore, in the surface inspection of the scratch or the like inaccordance with the present invention, the sensitivity must be ensured,and also whether the detected defect is classified correctly or not mustbe evaluated previously. The data must be sampled based on not only thedetected luminance information but also discrimination processingresult. In detail, it is important that only the doubtful defect that islocated near the discrimination line (threshold value) 20 or 50 isselected from among many detected defects and only the selected defectis reviewed by use of a SEM apparatus (not shown in the drawing), thatis, only the doubtful defect is subjected to the review selectively forefficient evaluation. As described herein under, the defect of doubtfulclassification that is located near the discrimination line (thresholdvalue) 20 or 50 displayed on the screen 40 of the display unit 33 isspecified. Thereby, the positional coordinate of the defect is acquired.The wafer 10 is placed on a SEM apparatus and the above-mentioned defectis observed by means of SEM based on the acquired positional coordinate,and whether the defect is a foreign object or a scratch 23 of variousconfiguration is evaluated. Then, the review evaluation result obtainedby means of the SEM apparatus is supplied to the whole control unit 9through, for example, the network 34 and stored in the memory unit 31.Thereby, it is possible to review the validity of the discriminationline (threshold value) 20 or 50.

The screen 40 displayed on the display unit 33 is composed of a scratchdiscrimination luminance distribution graph 41, a large scratchdiscrimination luminance distribution graph 42, a correspondingcoordinate search on defect map 43, and a discrimination result displaywindow 44 as shown in FIG. 21. The scratch discrimination luminancedistribution graph 41 shows the relation between the received luminanceS(i) with the epi-illumination and the received luminance T(i) with theslant illumination, and shows the state that the defect is discriminatedbetween the small scratch 23 a group and the foreign object 24/largescratch 23 b group by means of the threshold (discrimination line) 20.The large scratch discrimination luminance distribution graph 42 showthe relation between the maximum luminance (ΣSa(i)) and the orthogonalluminance ratio (ΣSa(i)/ΣSb(i)), and shows the state that the defect isdiscriminated between the foreign object 24 group and the large scratch23 b group by means of the threshold (discrimination line) 50. Thecorresponding coordinate search on defect map 43 shows the generationstate of the scratch 23 and the foreign object 24 on the wafer 10(defect map). The discrimination result display window 44 shows thenumber of foreign object 24 and the number of scratches (tire mark 23aa, dimple mark 23 ab, rough surface 23 ac, large scratch 23 b, hugescratch 23 c) 23 corresponding to the size (small, medium, and large).The discrimination result display window 44 may be represented in theform of histogram.

The case in which four types of display contents are displayedseparately in individual windows is described hereinabove, but the casein which a plurality of graphs are displayed in one window may beemployed. Otherwise, the four types of display contents may displayednot simultaneously. The luminance ratio screen that is obtained byanalyzing the scratch content by use of the horizontal and verticalluminance ratios may be displayed by selecting it on the pull down menuthough it is not shown in the drawing. It may be possible to display thedefect coordinate, discrimination result, and the received luminance ofeach of the photoelectric converters 7 a to 7 i in one or a plurality ofitems by pointing the defect on the defect map with a cursor or the likein the corresponding coordinate search on defect map 43. Furthermore, onthe one of the scratch discrimination luminance distribution graph 41and the large scratch discrimination luminance distribution graph 42, oron both the graphs, it may be possible that the data corresponding tothe defect pointed by use of a cursor or the like is blinked, color ofthe data is changed, or the size of the display mark is changed so thatan operator can easily recognize the corresponding data. Furthermore, itmay be possible that, when the data point is selected by use of an inputmeans 32 such as a cursor or the like on the scratch discriminationluminance distribution graph 41 or the large scratch discriminationluminance distribution graph 42, the display mark is blinked, the coloris changed, or the size of the display mark is changed on the defect mapso that an operator can easily discriminate the corresponding data fromother data on the monitor 33. Furthermore, one or a plurality ofinformation of the defect coordinate, discrimination result, andreceived luminance of each of the photoelectric converters 7 a to 7 i ofthe data specified on the graphs 41 and 42 may be displayed. Asdescribed hereinabove, an arbitrary defect data is selected on the graph41 or 42 or the defect map 43 and the specified inspection informationis displayed on the monitor 33. Thereby, it is possible to complete theexamination of the validity of the discrimination processing within ashort time.

As described hereinabove, it is possible to display the inspectionresult stored in the memory unit 31 (the coordinate data of the foreignobject 24 and the scratch 23, discrimination result of the foreignobject 24 and various scratch 23, and received luminance data obtainedfrom the photoelectric converters 7 a to 7 i with the epi-illuminationand the slant illumination) on the screen of the display unit 33, and itis possible to review whether the detected defect is classifiedcorrectly or not. Particularly, it is possible to review the validity ofthe discrimination line (threshold value) 20 or 50 served fordiscrimination on the graph displays 41 and 42.

Furthermore, as shown in FIG. 21, the size of the defect of eachclassification of the foreign object 24 and the scratch 23 is estimatedcorrespondingly to the magnitude of the received luminance obtained fromthe photoelectric converters 7 a to 7 i as shown in the discriminationresult 44, the defect is classified into some categories, and thefrequency of the defect is displayed category-wise. This method iseffective for efficient use of the inspection result. The foreign object24 and scratch 23 that is sufficiently smaller than the design value ofthe semiconductor such as wiring interval (the size is very small)seldom affect the function of the product fatally. On the other hand,when many very large defects occurs (having large size), the productionmust be shutdown immediately. In other words, the countermeasure isdifferent depending on the size of the detected defect. Then, as shownin the discrimination result 44, the defect is categorized into threecategories, namely small size defect, medium size defect and large sizedefect. The small size defect is the very small defect that is notfatal, the medium size defect is the defect that is apt to result infatal result, and the large size defect is the defect that results infatal result inevitably. The number of categories is by no means limitedto three, but may be one or a plurality of categories arbitrarilydepending on the application. Three categories are set for all theclassifications of the foreign object 24 and the scratch 23, but thedifferent number of categories may be set for each classification of theforeign object or scratch. The subtotal may be calculated for eachcategory. The total may be calculated for the foreign object 24 and thescratch 23 respectively. The total number of defects of the foreignobject 24 and the scratch 23 may be displayed.

As described hereinabove, the whole control unit 9 is structured so asto generate the subtotal for the foreign object 24 category and variousscratch 23 category or the total as the discrimination result 44.Thereby, it is possible to manage the subtotal for these categories andthe total number when the present invention is introduced to themanufacturing process, and as the result it is possible to monitor theoccurrence of the scratch 23 and foreign object 24 efficiently, and thesuitable countermeasure can be applied.

Furthermore, the whole control unit 9 is provided with a frequencydistribution display function to show the defect size distribution indetail. As shown in FIG. 22, the abscissa represents the receivedluminance when the epi-illumination is irradiated and the ordinaterepresents the frequency. In FIG. 22, the frequency distribution isdisplayed only for the defect data that is classified as the tire mark23 aa. The frequency distribution may be displayed for the defect datathat is classified as each classification of the foreign object 24 andthe scratch 23, or for all the defect data that is recognized as thescratch, or for all the defect data including the foreign object 24 andthe scratch 23. Any of various combinations may be displayed. Though notshown in the drawing, any of various combinations can be selected bymeans of the pull down menu. The abscissa may represent the luminance ofeach of photoelectric converters 7 a to 7 i, or may represent thereceived luminance sum of the photoelectric converters 7 a to 7 i forarbitrary combination of these photoelectric converters 7 a to 7 i.Furthermore, the same processing may be performed for the slantillumination data. By using the frequency distribution display function,not only the defect distribution can be analyzed in detail but also thescattered light distribution can be analyzed easily in detail.

Furthermore, the exclusive analysis tool is effectively used to analyzethe inspection data, and also the commercially available spreadsheetsoftware that is used for various calculation may be easily usedeffectively to shorten the evaluation time. Then, the entire inspectiondata or selected partial inspection data is saved for the items shown inFIG. 23 in the memory unit 31 such as hard disk or floppy disk in theformat that is readable by use of the spreadsheet software. In thepresent example, the identification number given to the defect,discrimination result, received luminance obtained by means of each ofthe photomultipliers 7 a to 7 i when the epi-illumination is irradiated,and the received luminance obtained by means of each of thephotomultipliers 71 to 7 i when the slant illumination is irradiated arewritten in the memory unit 31. Not all these data are necessary. In somecases, it is meaningful to save the defect coordinate data. By readingthe data by use of the commercially available spreadsheet software, thewhole control unit 9 is made possible to analyze the data of thedetected defect easily, and the discrimination capability is improvedwithin a short time.

The method in which a plurality of photoelectric conversion means 7 a to7 i is used to evaluate the three-dimensional intensity distribution ofthe diffracted light is described hereinabove.

Next, the third example of a surface inspection apparatus for inspectingthe scratch or the like served to obtain the two-dimensionaldistribution of the diffracted light easily will be described withreference to FIG. 24 to FIG. 26B. The present example shows an apparatusthat is formed by adding a detection optical system comprising lenses108 and 106, CCD cameras 104 and 107 and a beam splitter 105 to the highangle detection optical system 5 a in the example shown in FIG. 1 orFIG. 9. Therefore, also in the present example, there are theepi-illumination system and the slant illumination system, and thedefect is discriminated between the foreign object 24 and the smallscratch 23 a based on the luminance ratio. The two-dimensionalphotoelectric conversion means such as TDI sensor may be used as theadded CCD cameras 104 and 107. Furthermore, though two CCD cameras 104and 107 are used in the present example, the structure in which one CCDcamera is moved to two positions, namely the image forming plane and theFourier transformation plane, may be employed. The one CCD camera 104 islocated so that the image forming plane of the camera is coincident withthe image forming plane of the lens 108. The other CCD camera 107 islocated so that the image forming plane of the camera is coincident withthe Fourier transformation plane of the lens 106.

At first, in the computing unit 18 a of the computation processing unit8, by use of the image forming data, which is obtained by means of theCCD camera 104, ND converted by means of the A/D conversion unit 16 a,and stored in the memory unit 17 a, for example, the signal that isconverted to the binary signal with a desired threshold value forindicating the defect is extracted to thereby search the position of thedefects 23 and 24, and the searched result is supplied to and stored inthe memory unit 31 as the positional coordinate of the defects. Thewhole control unit 9 controllably drives the stage 15 according to thecontrol command supplied from the stage controller 14 based on thepositional coordinate of the searched defects, and positions the defects23 and 24 at the visual field center of the CCD camera 107.

Next, the computing unit 18 b of the computation processing unit 8performs the evaluation as described herein under by use of the imagedata that is obtained by means of the CCD camera 107, ND-converted bymeans of the ND conversion unit 16 a, and stored in the memory unit 17a. For example, in the case that there is a linear defect like the largescratch 23 b in the horizontal direction as shown in FIG. 25A, thediffracted light is distributed in the vertical direction in FIG. 25B onthe Fourier transformation plane. It becomes possible that thehorizontal diffracted light distribution is evaluated by evaluating byuse of the algorithm shown in FIG. 26. At first, in the computing unit18 b, eight luminance evaluation regions that are indicated with circlesin FIG. 25B are set around the point where zero order diffracted lightis received as shown in FIG. 25A. The luminance evaluation region is acircle in the present example, but the region is not necessarilycircular. The region may be quadrangular or polygonal. Furthermore,eight luminance evaluation regions are set in the present example, butthe number of regions may be more or less depending on the accuracy forevaluation of the scattered light intensity distribution. The number andthe configuration of the region are by no means limited. Then, thecomputing unit 18 b calculates the received light sum (Si) of each pixelin each set luminance evaluation region. The horizontal diffracted lightdirectionality is evaluated according to the process flow S65, S66, andS67 shown in FIG. 26 by use of eight luminance sums in the same manneras used in the method shown in FIG. 15 or FIG. 17. The light of thelight source 2 is irradiated from the direction near the normal line ofthe wafer 10 in the present example, but the light may be irradiatedfrom the slant direction. The diffracted light in the normal linedirection of the wafer 10 is received in the present example, but thediffracted light in the slant direction may be received. The pseudoperpendicular illumination obtained by locating the reflection mirror 4c at the position outside the NA of the lens 108 so that the regularreflected light reflected from the wafer 10 is not received is used inthe present example, but the perpendicular illumination may be used.

The case in which the method is applied to a wafer 10 having no wiringpattern is mainly described hereinbefore. When this method is applied toa wafer 10 having wiring pattern, a space filter 208 is provided asshown in FIG. 27. However, in some cases, the space filter is notnecessarily required depending on the case. In the present example, thecase in which it is required to remove the diffraction pattern based onthe diffracted light emitted from the periodical wiring pattern by useof, for example, a linear space filter as described in JapaneseUnexamined Patent Publication No. H6-258239 will be described. Thestructure of the present example will be described with reference toFIG. 27. The present example is provided with a wafer 10 that is anobject to be inspected, an illumination unit comprising a light source2, an optical path switching mechanism 3, reflection mirrors 4 a″, 4 b,4 a′, 4 a, and 4 c′, and a detection unit comprising a lens 6, a spacefilter 208, and photoelectric conversion means 7. In the presentexample, one light source 2 is switched between the epi-illumination 12and the slant illumination 11 by use of the optical path switchingmechanism 3 and the reflection mirrors 4 a″, 4 b, 4 a′, and 4 a, but thenumber of light sources and the number of reflection mirrors are by nomeans limited. The number of light sources may be smaller or larger thantwo. The same discrimination principle and discrimination processingmethod as applied to the above-mentioned examples are applied also tothe present example. The any one of perpendicular illumination andpseudo perpendicular illumination shown in FIG. 7A to FIG. 7D may beused as the epi-illumination.

The defect is discriminated between the scratch 23 and the foreignobject 24 by analyzing the distribution and the intensity of thescattered light emitted from the scratch 23 based on the specificconfiguration of the scratch by use of the computation processing unit 8in the method described hereinbefore. Furthermore, the configuration ofthe scratch 23 is classified in detail.

Next, the fourth example of a surface inspection apparatus forinspecting the scratch or the like served to realize the firstembodiment in accordance with the present invention will be describedwith reference to FIG. 28 to FIG. 34. In detail, in the fourth example,the defect is discriminated between the concave and the convex based onthe fact that the foreign object 24 is convex and the scratch 23 isconcave inherently. To say to avoid the misunderstanding again, theabove-mentioned discrimination method between the foreign object 24 andthe scratch 23 does not involve the discrimination between the convexand the concave, but involves discrimination based on the difference inaspect ratio between the width W and the depth D or height of thescratch 23 and the foreign object 24.

The fourth example is provided with an illumination optical systemcomprising a light source 300 and a half mirror 302 for illuminatingfrom the perpendicular direction of the wafer 10, a detection opticalsystem comprising a behind phase filter 305 located on the Fouriertransformation plane, an ahead phase filter 306, a beam splitter 304 forsplitting the light that passes through the filters 305 and 306, andphotoelectric conversion means 307 and 310, and a computation processingunit 8 comprising a differential signal processing unit 308 for makingthe difference between detected luminance obtained from thephotoelectric conversion means 307 and 310 and a discriminationprocessing unit 309 for recognizing the convex and the concave based onthe differential signal. In the fourth example, the photomultiplier A310and the photomultiplier B307 are used as the photoelectric conversionmeans. At first, the behind phase filter 305 and the ahead phase filter306 are described with reference to FIGS. 29A and 29B and FIG. 30. Thebehind phase filter 305 delays the phase of the light that passes nearthe region with respect to the periphery where the zero order diffractedlight passes. In detail, an optically flat plate having a thickness of twith additional thickness d on the region where the zero orderdiffracted light passes is used. The optical path length L on theperiphery and the optical path length L′ on the region where the zeroorder diffracted light passes are calculated according to the equation 2and the equation 3 respectively, wherein n denotes the refractive indexof the plate and n₀ denotes the refractive index of air.L=n×t+n ₀ ×d  (equation 2)L′=n×(t+d)  (equation 3)

In other words, the optical path length of the light that passes theperiphery and the optical path length of the light that passes theregion where the zero order diffracted light passes make the opticalpath difference ΔL1 represented by the following equation 4.ΔL1=L′−L =(n−n ₀)×d  (equation 4)

The refractive index of the air is assumed to be 1 and the refractiveindex is approximately 1.5 when glass material is used for the plate.Therefore, the optical path length difference ΔL is represented by thefollowing equation 5 in detail.ΔL1=(1.5−1)×d=0.5×d  (equation 5)

On the other hand, the ahead phase filter 306 has a thin thickness of(t−d) on the region where the zero order diffracted light passes asshown in FIG. 30. Such structure makes the optical path lengthdifference ΔL2 as represented by the equation 6 in the same manner asdescribed hereinabove.ΔL2=(n ₀ −n)×d  (equation 6)

In the above-mentioned detailed case, the optical path length ΔL2 isrepresented by the equation 7 in detail.ΔL2=−0.5×d  (equation 7)

In the case of the light source having a wavelength of λ, the light thathas passed the region of the zero order diffracted light has the behindphase of θ1 (rad.) and the ahead phase of θ2 (rad.) with respect to theperipheral passing light as represented by the equation 8 and theequation 9.θ1=ΔL1/λ×2π=(n−n ₀)×d/λ×2π  (equation 8)θ2=ΔL2/λ×2π=(n−n ₀)×d/λ×2π  (equation 9)

In the case that a light source for emitting the light having awavelength λ=488 nm is used, the phase deviation is equal to thedetailed value represented by the following equation 10 and equation 11in the above-mentioned detailed example.θ1=0.5×d/488×2π  (equation 10)θ2=−0.5×d/488×27π  (equation 11)

To make the behind phase θ1 and the ahead phase θ2 to be the phasedeviation of θ1=π/2 and θ2=−π/2 respectively, d may be the valuerepresented by the following equation 12 and equation 13.θ1=π/2=0.5×d/488×2π

Therefore, d=244 nm (equation 12)θ2=−π/2=−0.5×d/488×2π

Therefore, d=244 nm (equation 13)

As described hereinabove, the discrimination principle fordiscriminating between the scratch 23 and the foreign object 24, thatwill be described herein under, can be realized by use of the phasefilters 305 and 306 designed as described hereinabove.

The discrimination principle for discriminating between the foreignobject 24 and the scratch 23 will be described with reference to FIG.31. The laser irradiated onto the wafer 10 is a plane wave having thesame phase. The light regularly reflected from the wafer surface havingno defect is also a plane wave having the same phase. The regularreflected light is referred to as reference reflected light. The opticalpath length of the light reflected from the foreign object 24, namelythe convex, is shorter than that of the reference reflected light.Therefore the phase of the reflected light emitted from the convex isahead with respect to the phase of the reference reflected light. On theother hand, the optical path length of the reflected light from thescratch 23, namely the concave, is longer than that of the referencereflected light by the indent, and the phase is behind. In other words,when a light flux 12 is irradiated on the surface having the convex andconcave, the phase of the light reflected from the concave and theconvex is behind for the concave and ahead for the convex respectivelywith respect to the phase of the laser reflected from the flat portion.Then, in the present invention, two types of phase filters 305 and 306are inserted on the Fourier transformation plane, the differentialsignal processing unit 308 detects the ahead phase and the behind phasedue to the concave and the convex respectively, and the discriminationprocessing unit 309 discriminate the defect based on the detected aheadand behind phase. Thereby, the defect is discriminated between theforeign object 24 and the scratch 23. The data obtained as describedhereinabove is stored in the memory unit 31 connected to the wholecontrol unit 9 together with the positional coordinate data.

Furthermore, the details are described with reference to FIG. 32 to FIG.34.

At first, the differential signal intensity served for detecting thescratch 23, namely the concave, by means of the differential signalprocessing unit 308 and the discrimination processing unit 309 of thecomputation processing unit 8 will be described in detail herein underwith reference to FIG. 32. In the phase vector diagram, the clockwisedirection represents the behind phase and the anticlockwise directionrepresents the ahead phase with respect to the reference phase of thereference reflected light having the phase that has not been changed.The photomultiplier A310 receives the light that has passes through theahead phase filter 306. On the other hand, the photomultiplier B307receives the light that has passes through the behind phase filter 305.The regular reflected light component coming from the wafer surface isconverged at the point on the Fourier transformation plane and passesthrough the phase change region formed at the center of the phasefilter. As the result, the phase of the reference light that has passedthrough the ahead phase filter 306 becomes the vector 321 that is ahead90 degrees anticlockwise on the phase vector diagram. On the other hand,the scattered light emitted from the scratch 23 becomes theapproximately parallel light at the Fourier transformation plane andpasses through the peripheral region of the phase filters 306 and 305.

Therefore, the scattered light emitted from the scratch 23 having thebehind phase with respect to that of the reference transmitted lightbecomes the vector that deviates clockwise as shown on the left side ofthe phase vector diagram shown in FIG. 32. An image is formed by meansof interference between the reference reflected light 321 having theahead phase and the scattered light 231 having the behind phase on theimage forming plane. It is the sum of the reference light vector 321having the phase that has been made 90 degrees ahead by means of thephase filter 306 and the scattered light vector 231 having the phasethat has been made behind by means of the concave on the phase vectordiagram, and represents the image forming vector that arises from theinterference of the photomultiplier A detected light vector 310 a shownin FIG. 32. In other words, the luminance of the formed image isrepresented by the length of the photomultiplier A detected light vector310 a.

Similarly, the luminance of the formed image that has passes through thebehind phase filter 305 is represented by the phase vector of the sum ofthe reference light vector 322 having the phase that has been made 90degrees behind by means of the phase filter 305 and the scattered lightvector 231 having the phase that has been made behind by means of theconcave, namely the photomultiplier B detected light vector 307 a on theright side. The photomultiplier B detected light vector 307 a is largerthan the photomultiplier A detected light vector 310 a. That is, themagnitude of the synthetic vector formed by deviating the phase of thereference light in the same direction as that of the phase deviation ofthe scattered light detected by means of the photomultiplier B307 islarger.

Therefore, the differential signal processing unit 308 of thecomputation processing unit 8 subtracts the photomultiplier B detectedluminance 307 a from the photomultiplier A detected luminance 310 a togive a negative differential signal. Based on the negative differentialsignal, the discrimination processing unit 309 discriminates the defectas the scratch 23, namely the concave.

In FIG. 34, an example of a dark field image in which, a two-dimensionalphotoelectric conversion means, for example, a CCD camera is used as thephotoelectric conversion means 310 and 307 is used is shown. Eachluminance distribution shows the luminance profile on the a-a′ crosssection and b-b′ cross section on the image data. The left side diagramof FIG. 34 shows the case of the scratch 23. The dark field image thathas passed through the ahead phase filter 306 is darker than the darkfield image that has passed through the behind phase filter 305. Asdescribed hereinabove, in the case that the two-dimensionalphotoelectric conversion means is used, the differential signalprocessing unit 308 of the computation processing unit 8 may calculatethe difference of the maximum value in the detected luminance profile.

Next, the differential signal intensity for detecting the foreign object24, namely the convex, by means of the differential signal processingunit 308 and the discrimination processing unit 309 of the computationprocessing unit 8 will be described in detail with reference to FIG. 33.The phase of the scattered light 241 is made ahead with respect to thephase of the reference light in the case of the foreign object 24,namely the concave. Therefore, the intensity on the image forming planeof the received light 310 b that has passed through the ahead phasefilter 306 received by mean of the photomultiplier A310 is stronger thanthe intensity of the received light 307 b that has passed through thebehind phase filter 305 received by means of the photomultiplier B307.As the result, the differential signal processing unit 308 gives thepositive differential signal. Based on the positive differential signal,the discrimination processing unit 309 discriminates the defect as theforeign object 24, namely the convex.

Furthermore, as shown on the right side of FIG. 34, in the case of theforeign object 24, the dark field image that has passed through theahead phase filter 306 is brighter. As described hereinabove, in thecase that the two-dimensional photoelectric conversion means is used,the differential signal processing unit 308 of the computationprocessing unit 8 may calculate the difference of the maximum value inthe detected luminance profile.

As described hereinabove, the differential signal of the luminancesignal obtained from the differential signal processing unit 308 changesbetween negative and positive depending on the concave and convexconfiguration of the defect including the scratch 23 and the foreignobject 24. Therefore, the discrimination processing unit 309 checkswhether the signal is negative or positive to thereby discriminatewhether the defect is a scratch 23 or a foreign object 24. Furthermore,it is possible that the discrimination processing unit 309 converts thedifferential signal intensity to the depth or height information easily.

Only the case in which the scratch 23 is included as the defect type isdescribed in the fourth embodiment described hereinabove. Theconfiguration is classified by means of the directionality of thediffracted light only in the case of the defect that has been previouslyclassified as the scratch 23 or only in the case of the defect that hasbeen previously classified as the foreign object 24 in the front half ofthe first to fourth embodiments. However, as a matter of course, thecomputation processing unit 8 can easily realize the configurationclassification of the defect by use of the classification function basedon the directionality for the defect including only the foreign object24 and for the defect including only the scratch 23. Furthermore, it ispossible to combine the convex/concave discrimination method based onthe phase difference described in the rear half of the first to fourthembodiments and the diffracted light distribution evaluation methoddescribed in the front half of the first to fourth embodiments.

According to the invention described hereinabove, ADC (Automatic DefectClassification) or on-the-fly ADC in which the type of the defect isclassified synchronously or asynchronously with the defect detectionwhile the defect is being detected is realized.

Next, an embodiment for inspecting the defect located near the waferedge will be described with reference to FIG. 35 to FIG. 40.

At first, the case in which the present embodiment is applied to theconverging detection optical system shown in FIG. 10, FIG. 11A, and FIG.11B. In detail, FIG. 35 shows the case in which a defect 402 such as ascratch 23 or a foreign object 24 adheres near the wafer edge 403. Inthis case, when the illumination light 11 or 12 such as a laser isirradiated onto the defect 402 such as the scratch 23 or the foreignobject 24, the edge 403 is included in the light flux d. Furthermore,the scattered light emitted from the wafer edge 403 distributes on thevertical plane in the normal line direction of the edge as shown in FIG.36. As the result, as shown in FIG. 37, the scattered light 404 emittedfrom the edge 403 of the wafer 10 distributes in the edge normal linedirection with strong directionality in the down view from the placeabove the wafer 10. The scattered light 405 emitted from the defect 402does not exhibit remarkable directionality. Therefore, as shown in FIG.38, one or two detection optical systems located in the edge tangentialdirection, namely the B detection optical system and B′ detectionoptical system in FIG. 38, are used to detect the scattered light 405emitted from the defect 402 with stronger intensity than that of thescattered light 404 emitted from the edge 403. Otherwise, one or aplurality of detection optical systems selected from C detection opticalsystem, C′ detection optical system, D detection optical system, and D′detection optical system may be used as the detection optical system.Furthermore, the comparison computing unit 18 in the computationprocessing unit 8 calculates the detected luminance ratio between Adetection optical system, A′ detection optical system, andabove-mentioned detection optical systems to thereby determine themagnitude of the directionality. Thereby, whether there is the defectincluding only the edge 403 or the defect including the defect 402 isdetermined.

Next, the case in which the present embodiment is applied to the imageforming detection optical system shown in FIG. 24 will be described withreference to FIG. 39. In this case, a space filter 407 shown in FIG. 40is located on the Fourier transformation plane and a space filtershading unit 408 is located in the wafer edge normal line direction. Asshown in FIG. 36, the scattered light emitted from the wafer edge 403distributes from the wafer edge 403 to the normal line direction withstrong directionality. Therefore, the space filter 407 is inserted tothereby shade the scattered light emitted from the edge 403, and it ispossible for the photoelectric conversion means 107 to receive thescattered light emitted from the defect 402.

In the present embodiment, the case in which an Rθ stage (stage that isrotatable in the horizontal plane) is used as the stage 15. In thiscase, the direction of the detection optical system and the wafer edgeirradiated with the illumination light such as a laser light isrelatively stable and constant including orientation flat. Therefore, itis not necessary to change the position of the detection optical systems5 b and 5 c to be used in the converging optical system or the shadingdirection of the space filter 407 in the image forming optical system.

Only an X-Y stage is used as the stage 15, it is necessary to change thedetection optical systems 5 b and 5 c that are used in matching with theedge direction of the wafer or to reverse the space filter 407.

As described, according to the above examples, the foreign objectlocated near the wafer edge can be detected at high sensitivity, andmalfunction of the process in which the foreign object is apt to adhereon the peripheral region of the edge is found immediately. As theresult, the high yield production can be achieved.

According to the present invention, when a work target such asinsulating film is subject to a polishing process such as CMP or agrinding process in the semiconductor/magnetic head manufacturingprocesses, the present invention exhibits the effect that the scratch ofvarious configurations and the adhered foreign object that occur on thesurface are inspected discriminatingly. The present invention makes itpossible for the configuration of the scratch to be classified in detailand the cause of the malfunction found promptly. The present inventionmakes it possible for malfunction of the polishing apparatus to be foundpromptly because the total inspection or high frequency samplinginspection can be carried out and a prompt and suitable countermeasureapplied, making it possible to improve the yield remarkably. Theinvention may be embodied in other specific forms without departing fromthe sprit or essential characteristics thereof. The present embodimentis therefore to be considered in all respects as illustrative and notrestrictive, and all changes which come within the meaning and range ofequivalency of the appended claims are therefore intended to be embracedtherein.

What is claimed is:
 1. A surface inspection apparatus, comprising: astage configured to support an inspection target mounted thereupon: afirst illumination optical system configured to illuminate from a firstangle the inspection target mounted on the stage; a second illuminationoptical system configured to illuminate from a second angle having alower elevation angle than the first angle, the inspection targetmounted on the stage; a reflection light detection system configured todetect a first reflected light reflected from the inspection targetafter being illuminated by the first illumination optical system, toconvert the first reflected light to a first luminance data, to detect asecond reflected light reflected from the inspection target after beingilluminated by the second illumination optical system, and to convertthe second reflected light to a second luminance data; a defectclassification system configured to recognize first luminance data andsecond luminance data arising from positions located in close proximityto each other as data of a concatenated defect, and to classify a linearconcatenated defect as a scratch by referring to the logical sum of saidfirst luminance data and said second luminance data; and an outputportion configured to output information of the type of the detectclassified in the effect classification system.
 2. The surfaceinspection apparatus according to claim 1, wherein said defectclassification system is configured to perform recognition by referringto the logical sum of said first luminance data and said secondluminance data.
 3. The surface inspection apparatus according to claim1, wherein said defect classification system is configured to recognizefirst luminance data arising from positions located in close proximityas data of a concatenated defect, and to classify a linear concatenateddefect recognized thereby as a scratch; and wherein said defectclassification system is configured to recognize second luminance dataarising from positions located in close proximity as data of aconcatenated defect and to classify a linear concatenated defectrecognized thereby as a scratch.
 4. The surface inspection apparatusaccording to claim 3, wherein said defect classification system isconfigured to remove the data classified as a scratch, and to classifydata of the scratch and data of a foreign object by non-removal date. 5.The defect inspection apparatus, as described in claim 1, wherein saidreflection light detection system comprises: a first detection systemconfigured to detect reflection light reflected from the second angle;and a second detection system configured to detect reflection lightreflected from a third angle having a lower elevation angle than thesecond angle; and wherein said defect classification system isconfigured to classify a type of defect by using non-removal datadetected by the first and second detection system.
 6. The defectinspection apparatus, as described in claim 1, wherein, at least, one ofsaid plurality of first detectors is set to adjust sensitivity.
 7. Thedefect inspection apparatus, as described in claim 1, wherein, at least,one of said plurality of second detectors is set to adjust sensitivity.8. The defect inspection apparatus, as described in claim 1, wherein thedefect inspection apparatus includes an optical path switchingmechanism, which switches the illumination by said first illuminationoptical system and the illumination by said second illumination opticalsystem.
 9. The defect inspection apparatus, as described in claim 1,wherein a light source for said first illumination optical system isidentical to a light source for said second illumination optical system.10. The defect inspection apparatus, as described in claim 1, whereinsaid plurality of first detectors are photomultipliers.
 11. The defectinspection apparatus, as described in claim 1, wherein said signalprocessing system inspects a defect by using the sum of signals detectedfrom said plurality of first detectors.